JavaScript

You can use a .js file in the ECMAScript compliant JavaScript language to define the service logic of an HML page. With dynamic typing, JavaScript can make your application more expressive with a flexible design. The following describes the JavaScript compilation and running.

Syntax

The ES6 syntax is supported.

• Module declaration

  Import functionality modules.

  import router from '@ohos.router';
  

• Code reference

  Import JavaScript code.

  import utils from '../../common/utils.js';
  

Objects

• Application objects |Name|Type|Description| |--------|--------|--------| |$def|Object|Object that is exposed in the app.js file and obtained by this.$app.$def.
  NOTE
  Application objects do not support data binding. Data update should be triggered on the UI.|

  Example

  // app.js
  export default {
    onCreate() {
      console.info('Application onCreate');
    },
    onDestroy() {
      console.info('Application onDestroy');
    },
    globalData: {
      appData: 'appData',
      appVersion: '2.0',
    },
    globalMethod() {
      console.info('This is a global method!');
      this.globalData.appVersion = '3.0';
    }
  };
  

  // index.js
  export default {
    data: {
      appData: 'localData',
      appVersion:'1.0',
    },
    onInit() {
      this.appData = this.$app.$def.globalData.appData;
      this.appVersion = this.$app.$def.globalData.appVersion;
    },
    invokeGlobalMethod() {
      this.$app.$def.globalMethod();
    },
    getAppVersion() {
      this.appVersion = this.$app.$def.globalData.appVersion;
    }
  }
  

• Page objects |Name|Type|Description| |--------|--------|--------| |data|Object/Function|Data model of the page. If the attribute is of the function type, the return value must be of the object type. The attribute name cannot start with a dollar sign ($) or underscore (). Do not use reserved words (for, if, show, and tid).
  Do not use this attribute and private or public at the same time.| |$refs|Object|DOM elements or child component instances that have registered the ref attribute. For example code, see Obtaining a DOM element.| |private|Object|Data model of the page. Private data attribute can be modified only on the current page.| |public|Object|Data model of the page. Behaviors of public data attributes are the same as those of the data attribute.| |props|Array/Object|Used for communication between components. This attribute can be transferred to components via <tag xxxx='value'>. A props name must be in lowercase and cannot start with a dollar sign ($) or underscore (). Do not use reserved words (for, if, show, and tid). Currently, props does not support functions. For details, see props.| |computed|Object|Used for pre-processing an object for reading and setting. The result is cached. The name cannot start with a dollar sign ($) or underscore (_). Do not use reserved words. For details, see computed.|

Methods

• Data methods |Name|Parameter|Description| |--------|--------|--------| |$set|key: string, value: any|Adds an attribute or modifies an existing attribute.
  Usage:
  this.$set('key',value): Add an attribute.| |$delete|key: string|Deletes an attribute.
  Usage:
  this.$delete('key'): Delete an attribute.|

  Example

  // index.js
  export default {
    data: {
      keyMap: {
        OS: 'OS',
        Version: '2.0',
      },
    },
    getAppVersion() {
      this.$set('keyMap.Version', '3.0');
      console.info("keyMap.Version = " + this.keyMap.Version); // keyMap.Version = 3.0
  
      this.$delete('keyMap');
      console.info("keyMap.Version = " + this.keyMap); // log print: keyMap.Version = undefined
    }
  }
  

• Public methods |Name|Parameter|Description| |--------|--------|--------| |$element |id: string|Obtains the component with a specified ID. If no ID is specified, the root component is returned. For example code, see Obtaining a DOM element.
  Usage:
  <div id='xxx'></div>
  - this.$element('xxx')
  - this.$element('xxx'): Obtain the component whose ID is xxx.
  - this.$element(): Obtain the root component.| |$rootElement|N/A |Obtains the root element.
  Usage:
  this.$rootElement().scrollTo({ duration: 500, position: 300 }), which scrolls the page by 300 px within 500 ms.| |$root |N/A |Obtains the root ViewModel instance. For example code, see Obtaining the ViewModel.| |$parent |N/A |Obtains the parent ViewModel instance. For example code, see Obtaining the ViewModel.| |$child |id: string|Obtains the ViewModel instance of a custom child component with a specified ID. For example code, see Obtaining the ViewModel.
  Usage:
  this.$child('xxx'): Obtain the ViewModel instance of a custom child component whose ID is xxx.|

• Event methods |Name|Parameter|Description| |--------|--------|--------| |$watch|data: string, callback: string |Function|Listens for attribute changes. If the value of the data attribute changes, the bound event is triggered. For details, see Monitoring Data Changes by $watch.
  Usage:
  this.$watch('key', callback): triggers the callback event by listening for changes in the value of the key property.|

• Page methods |Name|Parameter|Description| |--------|--------|--------| |scrollTo⁶⁺|scrollPageParam: ScrollPageParam|Scrolls the page to the target position. You can specify the position using the ID selector or scrolling distance.|

  Table 1 ScrollPageParam⁶⁺

Name	Type	Default Value	Description
position	number	-	Position to scroll to.
id	string	-	ID of the element to be scrolled to.
duration	number	300	Scrolling duration, in milliseconds.
timingFunction	string	ease	Animation curve for scrolling. Available options: Animation Styles
complete	() => void	-	Callback to be invoked when the scrolling is complete.

Example

this.$rootElement().scrollTo({position: 0})
this.$rootElement().scrollTo({id: 'id', duration: 200, timingFunction: 'ease-in', complete: ()=>void})

Obtaining a DOM Element

1. Use $refs to obtain a DOM element.

   <!-- index.hml -->
   <div class="container">
     <image-animator class="image-player" ref="animator" images="{{images}}" duration="1s" onclick="handleClick"></image-animator>
   </div>
   

   // index.js
   export default {
     data: {
       images: [
         { src: '/common/frame1.png' },
         { src: '/common/frame2.png' },
         { src: '/common/frame3.png' }
       ]
     },
     handleClick() {
       const animator = this.$refs.animator; // Obtain the DOM element whose $refs attribute is animator.
       const state = animator.getState();
       if (state === 'paused') {
         animator.resume();
       } else if (state === 'stopped') {
         animator.start();
       } else {
         animator.pause();
       }
     },
   };
   

2. Call $element to obtain a DOM element.

   <!-- index.hml -->
   <div class="container" style="width:500px;height: 700px; margin: 100px;">
     <image-animator class="image-player" id="animator" images="{{images}}" duration="1s" onclick="handleClick"></image-animator>
   </div>
   

   // index.js
   export default {
     data: {
       images: [
         { src: '/common/frame1.png' },
         { src: '/common/frame2.png' },
         { src: '/common/frame3.png' }
       ]
     },
     handleClick() {
       const animator = this.$element('animator'); // Obtain the DOM element whose ID is animator.
       const state = animator.getState();
       if (state === 'paused') {
         animator.resume();
       } else if (state === 'stopped') {
         animator.start();
       } else {
         animator.pause();
       }
     },
   };
   

Obtaining the ViewModel

The following shows files of the root page:

<!-- root.hml -->
<element name='parentComp' src='../../common/component/parent/parent.hml'></element>
<div class="container">
  <div class="container">
    <text>{{text}}</text>
    <parentComp></parentComp>
  </div>
</div>

// root.js
export default {
  data: {
    text: 'I am a root!',
  },
}

Customize the parent component.

<!-- parent.hml -->
<element name='childComp' src='../child/child.hml'></element>
<div class="item" onclick="textClicked">
  <text class="text-style" onclick="parentClicked">parent component click</text>
  <text class="text-style" if="{{showValue}}">hello parent component!</text>
  <childComp id = "selfDefineChild"></childComp>
</div>

// parent.js
export default {
  data: {
    showValue: false,
    text: 'I am parent component!',
  },
  parentClicked () {
    this.showValue = !this.showValue;
    console.info('parent component get parent text');
    console.info(`${this.$parent().text}`);
    console.info("The parent component gets the child function.");
    console.info(`${this.$child('selfDefineChild').childClicked()}`);
  },
}

Customize the child component.

<!-- child.hml -->
<div class="item" onclick="textClicked">
  <text class="text-style" onclick="childClicked">Child component clicked</text>
  <text class="text-style" if="{{isShow}}">Hello child component</text>
</div>

// child.js
export default {
  data: {
    isShow: false,
    text: 'I am the child component!',
  },
  childClicked () {
    this.isShow = !this.isShow;
    console.info('child component get parent text');
    console.info('${this.$parent().text}');
    console.info('child component get root text');
    console.info('${this.$root().text}');
  },
}

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